Flat valve for hydraulic machine



March 8, 1966 v. BUDRYS ET AL 3,238,888

FLAT VALVE FOR HYDRAULIC MACHINE Filed NOV. 26, 1963 3 Sheets-Sheet 1 27- 4a 43 FI6.5

VITOIJS BUDRYS JACK RUBINSTEIN INVENTORS A ORNEY March 8, 1966 v, BUDRYS ET AL 3,238,888

FLAT VALVE FOR HYDRAULIC MACHINE Filed Nov. 26; 1963 5 Sheets-Sheet 2 I v/mus BUDRY JACK RUBINSTEIN INVENTORS .7 025 M TTORNEY March 8, 1966 v. BUDRYS ET AL 3,238,888

FLAT VALVE FOR HYDRAULIC MACHINE Filed Nov. 26, 1963 5 Sheets-Sheet 5 VITOLIS BUDRYS 5 JACK RUBINSTEIN INVENTORS ATTORNEY 3,238,838 FLAT VALVE FUR HYDRAULKC MACHHNE Vitoiis Budrys, lnglewood, Calif, and Jack Rubinstein, Milwaukee, Wis., assignors to The Oilgear Company Milwaukee, Wis.

Filed Nov. 26, 11963, Ser. No. 326,064 6 Claims. (Cl. 103-162) This invention relates to rotary hydraulic machines such as positive displacement hydraulic pumps and hydraulic motors in which pistons and cylinders are arranged in a cylinder unit and the pistons reciprocate as the cylinder unit rotates. Flow of liquid to and from the cylinders is distributed by a floating flat valve that has a pair of arcuate ports with which the cylinder ports alternately register.

The rotary cylinder unit has an odd number of cylinders and as the cylinder unit rotates, the number of cylinder ports in communication with each valve port continually changes such that a maximum share of the number of cylinder ports register with the pressure one of the valve ports and then a minimum share of the number of cylinder ports register with the pressure port. As a corollary thereto a minimum share of the cylinder ports register with the exhaust one of the valve ports and alternately a maximum share of the cylinder ports register with the exhaust one of the valve ports.

The flat valve is non-rotatably supported on a manifold portion of the pump or motor housing and makes sealing engagement therewith by means of hold-up motors provided in the flat valve under the valve ports, and these hold-up motors permit axial floating movement of the flat valve between the cylinder unit and the housing. The hold-up motors under the valve ports comprise hollow pistons through which manifold passages can conduct fluid to and from the arcuate valve ports. The hold-up motors under the valve ports being subject to the pressure of the fluid in their associated valve ports urge the valve toward the cylinder unit in opposition to hydraulic forces tending to separate the flat valve from the cylinder unit.

The hydraulic hold-up motors under the valve ports are constructed and arranged to balance the flat valve when the minimum number of cylinder ports register with a high pressure port of the flat valve and when the hydraulic forces tending to separate or blow off the fiat valve from the cylinder are a minimum. As a pressure loaded one of the cylinder ports enters On a bridge which is a portion of the flat valve between the valve ports, the separa tion forces on the flat valve begin to increase toward a maximum value which occurs when a maximum number of cylinder ports register with the high pressure valve port. Additional forces are then required to hold the flat valve against its valve seat. These additional forces are provided by auxiliary hold-up motors located in the flat valve under the bridge sections of the valve and these auxiliary hold-up motors are connected by passages in the valve to the face of the bridges. As the cylinder ports travel across the bridges they communicate with the auxiliary hold-up motors, and the present invention relates particularly to the arrangement of the ports in the face of the bridges to provide such communication for energization and de-energization of these auxiliary hold-up motors and for providing predetermined balance areas in the face of the bridges for predetermining in steps the separation forces that occur as a cylinder port crosses a bridge.

Auxiliary hold-up motors have been employed under bridges of a flat valve, but heretofore in order to substantially balance the gradually changing blow off forces that occur between the flat valve and a seat of the cylinder unit, the auxiliary hold-up motors have been employed to add additional hold-up force in steps from the minimum value of blow-oft forces to the maximum value of blow-off forces and were located so as to best balance the gradually United S tar-es l atent O lCc changing forces and tilting moments. In attempts to reduce the tilting moments that occur between minimum and maximum separation forces and attempts to minimize the difference between the separation forces and the hold-up forces, means have also been provided to simultaneously energize an auxiliary hold-up motor under one bridge while an auxiliary hold-up motor under the other bridge was also being energized. These arrangements as heretofore employed left much to be desired with respect to reducing the difference between the total of the hold-up forces and the separation forces and to substantially minimizing the tilting moments.

According to the present invention, however, the auxiliary hold-upmotors under one bridge are also energized sequentially to provide additional hold-up force in steps which are matched to corresponding stepped changes in the separation forces occurring on the face of that bridge. Thus, simultaneously with the energization of each auxiliary hold-up motor under one bridge, a balance port which is connected to the auxiliary hold-up motor and provides a predetermined area in the face of that bridge is energized by a pressure loaded cylinder port crossing the bridge and registering therewith, whereby the balance port immediately upon communication with the cylinder port extends the pressure field on the face of the bridge for a predetermined angular rotation of the cylinder barrel and this extended effective pressure field is maintained substantially constant over this angular distance so that the separation forces on the face of the bridge and the increased hold-up force provided by the corresponding energized auxiliary hold-up motor are substantially equal and opposite during this angular travel, thereby eliminating any moments tending to tilt the valve and also substantially balancing the hold-up forces wit-h the separation forces. The invention is embodied in a hydraulic pump or motor having a rotatable cylinder unit having cylinder ports circumferentially spaced in an end face of the cylinder unit, a flat valve arranged with a face in engagement with a seat provided on the end face of the cylinder unit, diametrically opposite high and low pressure ports in the valve with which the cylinder ports alternately register upon rotation of the cylinder unit, the intermediate circumferential portions of the valve between the ports being the bridges of the valve, hold-up motors under the ports of the valve and subject to the pressure in their associated ports for holding the valve against the cylinder unit, a plurality of auxiliary hold-up motors under each bridge and energized by cylinder ports crossing the bridges to aid the hold-up motors in holding the valve against the cylinder unit, characterized in that auxiliary hold-up motors are sequentially energized by each pressure loaded cylinder port crossing the associated bridge, and the corresponding ports in the face of the bridge for the auxiliary hold-up motors cooperating with the cylinder ports and being constructed and arranged to provide effective pressure area therewith to cause the increase in separation forces to occur in steps corresponding to the increase of the hold-up forces provided by the auxiliary hold-up motors.

It is therefore an object of the present invention to provide a hydraulic machine with an improved axially floating fiat valve held in sealing engagement with a valve seat on a rotatable cylinder unit by hydraulic means that maintains the valve balanced against tilting moments and separation forces for any operating pressure and any speed of rotation of the cylinder unit.

Another object of the invention is to provide such an axially floating flat valve in sealing engagement with the valve seat by making the change in the moments of the separation forces correspond to the changes in the moments of the hold-up forces so that the net positive 3 hold-up force required is of relatively very small magnitude.

Another object of the invention is to provide such a flat valve with effective balance areas in the face of the bridges so as to cause stepped changes in the pressure field on each bridge which are effectively opposed by corresponding stepped changes in the hold-up area of auxiliary hold-up motors under the bridge sections of the flat valve. And a further object of the invention is to arrange and construct such balance'areas that they may be provided by convenient and economical shop practices such as by drilling or by end milling.

Other objects and advantages will be apparent to one skilled in the art from the following description and accompanying drawings, in which:

FIG. 1 is a view in elevation and partly in section of a hydraulic machine with a floating type fiat valve embodying the present invention.

FIG. 2 is a view taken along the line 2-2 of FIG. 1 and showing a valve seat.

FIG. 3 is a view taken along the line 33 of FIG. 1 showing the face of a flat valve.

FIG. 4 is a view of the rear face of the flat valve shown in FIG. 3.

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 4 and shows a bridge piston and a holdup piston.

FIG. 6 shows curves of the effective areas or pressure fields occurring on the bridges of a flat valve not having balance port areas.

FIG. 7 shows curves corresponding to those of FIG. 6 but for a flat valve provided with balance port areas in the face of the bridges.

FIG. 8 shows curves of the stepped changes in the effective field area on the face of a leading bridge and corresponding changes in its hold-up field area for a flat alve as shown in FIG. 3.

FIG. 9 is a face view of another flat valve for use in the machine of FIG. 1 and taken along the line 9-9 thereof.

FIG. 10 is a face view of a portion of the valve of FIG. 9 including the upper bridge section shown on an enlarged scale with a cylinder port shown superimposed thereon.

FIG. 11 is a view of the back face of the flat valve of FIG. 9 and taken along the line 11-11 of FIG. 1; and

FIG. 12 is a cross-sectional view of the flat valve of FIGS. 9 and 11 taken along the line 12-12 of FIG. 11;

The invention may be embodied in any positive displacement hydraulic machine 10 having a rotatable cylinder unit in combination with an axially movable flat valve for distributing motive fluid to and from the cylinder unit. The hydraulic machine shown in FIG. 1 is an axial piston fixed displacement pump or motor, and comprises an angular shaped casing. A drive shaft 12 has a flange 13 mounted for rotation with the shaft in radial and thrust bearings, not shown, in a section 11 of the casing.

A cylinder unit or cylinder barrel 14 is rotatably supported against axial and radial movement in axially spaced bearings 16, 17 disposed on an axially extending stud or axle 18 in an end head 19 on the casing section 21. The axes of the shaft 12 of the cylinder barrel 14 are inclined to each other to determine the displacement or stroke of pistons 23 in cylinders 22 formed in the cylinder barrel. The pistons 23 are connected to the drive flange 13 by piston rods 24 whose ball shaped ends are held by ball sockets in the drive flange 13. The cylinder barrel has an odd number of cylinders circumferentially and uniformly spaced and wear plate 26 secured to the end of the cylinder barrel 14 which in a known manner provides cylinder ports 27 for the cylinders 22 and serves as a valve seat for a fluid distributing valve provided by a flat valve 28 secured by pins 29 to the end head 19 against rotation and for freedom of axial movement between the cylinder barrel and the end head.

The valve seat face of the wear plate 26 is shown in FIG. 2 and the face of the flat valve 23 adapted to make sealing engagement therewith is shown in FIG. 3. The face of the flat valve 28 is an annular surface defined between annular shoulders 30, and this valve face defines the limits of the pressure field area developed between the wear plate face and the flat valve face. The flat valve 28 is provided in its valve face wtih diametrically opposite arcuate slots which serve as valve ports 31, 32 with which the cylinder ports 27 alternately register upon rotation of the cylinder barrel. Valve port 31 has shallow port extensions 31a and 31b and valve port 32 has shallow port extensions 32a and 32b. Axial passages 33 in the flat valve are open to valve port 31 and extend through hollow pistons 37 of hold-up motors 36 which are urged by a spring 38 and fluid pressure to make sealing connection with axial passages 42 which join manifold passage 43 in the end head 19. Similarly, axial passages 34 in the flat valve are open to valve port 32 and extend through hollow pistons 41 of hold-up motors which make sealing connection with other axial passages, not shown, and which connect with another manifold passage, not shown. Manifold passage 43 leads to an external port 44 for the machine for bringing fluid to or from valve port 31, and the other manifold passage, not shown, similarly leads to an external port connection for bringing fluid to or from valve port 32.

The flat valve 28 is hydraulically balanced between the cylinder barrel and the end head by a hold-up system which produces hold-up forces acting between the valve and the end head which is operative to provide hold-up forces which are substantially equal and opposite to hydraulic separating forces between the valve seat 26 and the face of the fiat valve 28 which forms vary due to variations in the effective pressure field on the face of the flat valve.

The hold-up system comprises the four hold-up motors 36 and the four hold-up motors 40 and auxiliary motors 46, 47 located under the upper bridge of the flat valve and auxiliary motors 48 and 49 located under the lower bridge when viewed from the faces of the flat valve as shown in FIGS. 3 and 4. The hold-up motors 36, 40 comprise cylinders 41 formed in the back face of the valve in generally underlying relation and connected to their respective valve ports 31, 32. Each cylinder 41 has a hollow piston 37 urged by its spring 38 in sealing engagement with axial passages in the end head which are respectively aligned with the hold-up pistons 37 for through flow of motive fluid between valve ports and manifold passages.

The hold-up motors 36, 40 are arranged relative to their associated valve ports 31, 32 to provide a hold-up force substantially equal and opposite to the separating force on the valve when /2 of (Nl) cylinder ports, N being an odd number, are under pressure and the centroid of the separating forces lies on a diametrical line bisecting the valve ports. This is a condition for minimum separating force for the valve shown in FIG. 3 when five of the eleven cylinder ports 27 register with a high pressure one of the valve ports 31 or 32.

The auxiliary hold-up motors 46, 47 and 48, 49 are operative to provide additional hold-up force only when /2 of (Ni-l) cylinder ports are under pressure, as hereinafter described. These auxiliary hold-up motors comprise cylinders 50 formed under the bridges of the flat valve, FIG. 5, each having a solid or closed end bridge piston 51 so that the pressure of fluid in its cylinder urges the piston against the face of end head 19 and urges the valve against the valve seat.

The auxiliary hold-up motors are preferably located under the bridges at the radius of the valve ports so as to underlie the path of travel of the cylinder ports crossing the bridges. As shown in FIGS. 3, 4 however, the auxiliary hold-up motors are spaced generally circumferentially and are somewhat offset radially from the path of travel of the cylinder ports 27 on the bridges to properly space the bridge cylinders from each other and from the cylinders 41 for the hold-up motors so as not to weaken the structure of the flat valve. Balance ports 52, 53, 54, 55, are provided in the face of the bridges and comprise relatively large recess areas adapted to register with cylinder ports 27 crossing the bridges. The cylinders 5t) of the auxiliary hold-up motors are independently connected by passages 56 to the balance ports correspondingly located.

The four balance ports 52 through are located in the face of the bridges of the valve with two in each bridge and are constructed and arranged to subdivide the pressure field on the face of each bridge so that a pressure loaded cylinder port crossing the bridge causes a two step increase in the pressure field on the face of the bridge. For this purpose each balance port has a sufficient width and depth to provide unrestricted fluid flow therein so that when comtrnunicating with a cylinder port its pressure is immediately transmitted to the balance port.

While the area of the recess defining each balance port is smaller than the cross-sectional area of its associated bridge cylinder 50, the effective areas of the two are substantially equal for the effective area of a balance port includes the surrounding area in the face of the bridge subject to a pressure gradient. The mean effective field area of a balance port when communicating with a cylinder port causes a step change in the separating force between the valve and the wear plate that is substantially maintained until the cylinder port communicates with the next balance port when another step change occurs in the mean effective pressure field on the face of the bridge and this change is substantially maintained until the cylinder port communicates with the next valve port. Thus each bridge cylinder is maintained energized for a greater interval of time since its associated balance port communicates with a pressure loaded cylinder port for an extended distance of travel of the cylinder port on the face of the bridge.

Although a balance port upon initial communication with a pressure loaded cylinder port causes a sudden stepped increase in the separation forces between the fiat valve and wear plate, the auxiliary hold-up motor associated with this balance port provides a corresponding opposing hold-up force. The arrangement does not eliminate variations in separation forces but does minimize variations between separation and holdup forces. Thus, while the separating forces on the flat valve vary between minimum and maximum values in accordance with the position of the cylinder ports 27 on the flat valve 28, the change in separation forces occurring on each bridge are made to change in steps, by reason of the balance ports, and are simultaneously opposed by corresponding stepped changes in the hold-up forces by the energization of auxiliary hold-up motors 46, 47 or 48, 49 with their associated balance ports.

For facility in describing the operative relation of the flat valve 28 on its valve seat 26, the cylinder unit is assumed to be rotating in the direction of the arrow shown in FIGS. 2 and 3. A pressure loaded cylinder port is a cylinder port 27 moving from a high pressure valve port such as valve port 32 and the bridge toward which it is moving is a leading bridge. A first balance port 53 on the leading bridge is first to register with the pressure loaded cylinder port 27 and the second balance port 52 next registers therewith.

In FIG. 6 curve a illustrates the change in the pressure field area as a pressure loaded cylinder port 27 crosses a leading bridge of a fiat valve without balance ports, and curve b illustrates the simultaneous change in the pressure field area as a generally diametrically opposite cylinder port crosses the opposite or trailing bridge. In FIG. 7 curves c and d illustrate the modification in the effective pressure field areas of curves a and b from a gradual increase from minimum to maximum to a stepped increase effected by the balance ports 53, 52 and 55, 54, respectively, provided in the face of the bridges of flat valve 28. In FIG. 8 curve It illustrates the holdup area provided by the hold-up motors 36 and curve e the additional hold-up area provided by the auxiliary hold-up motors 47, 46 under one bridge which are energized simultaneously with their balance ports 53, 52 which provide the stepped changes in the opposing field area represented by curve c.

It can be seen from curve a that a pressure loaded cylinder port 27 would effect a varying increase in the pressure field for an angular span of travel of the cylinder port on the order of 30 degrees on the leading bridge, whereupon such cylinder port then communicates with port extension 31a of low pressure or exhaust port 31 of the flat valve. In order to substantially eliminate any difference between the gradually changing field and the opposing auxiliary hold-up areas, the balance ports provided effect, as shown by curve 0, stepped increases in the pressure field area on the leading bridge and as shown by curve e correspondingly maintain substantially equal and opposite auxiliary hold-up areas effective over this same angular span or travel of the pressure loaded cylinder port.

Thus in the graphical illustration a first or leading balance port 53 communicates with a pressure loaded cylinder port at about '24 degrees from the center of the bridge when the pressure loaded cylinder port has effectively begun to increase the separation forces. The leading balance port 53 and the pressure loaded cylinder port immediately cause a stepped increase in the effective pressure field and resulting separation forces as the pressure loaded cylinder port moves across the bridge. This stepped increase in the separation force is opposed by the auxiliary hold-up force provided by a first auxiliary hold-up motor 47 simultaneously energized with the leading balance port 53.

When such pressure loaded cylinder port is within l2 degrees from being centered on the bridge, where the center of the bridge is taken as zero degrees in the graphs, then it communicates with the second balance port 52 to immediately cause another stepped increase in the effective pressure field and in the resulting separation forces on the leading bridge to substantially the maximum value it will have when centered on the bridge. The second auxiliary hold-up motor is simultaneously energized with balance port 5'2 and together with the first auxiliary hold-up motor 47 provide additional hold-up forces equal and opposite to the increase in the separation forces on that bridge. Thus at successive positions of a pressure loaded cylinder port when resulting separation forces increase from a minimum to a maximum value, the two balance ports 53, 52 successively communicate therewith to provide a two step increase in the separation forces which is matched by the two step increase in the additional hold-up force provided by the corresponding auxiliary hold-up motors 4'7, Thus corresponding changes occur in the separation forces and in the hold-up forces which are made substantially equal and opposite to each other for each bridge of the valve.

It is a corollary to the above descri tion with respect to a leading bridge that the other bridge is a trailing bridge and that a cylinder port enters thereon from the low pressure or exhaust valve port 31 and crosses the trailing bridge to enter upon the high pressure valve port 32. A cylinder port entering a bridge from the exhaust valve port 31 first communicates with one balance port 54 and then with the second balance port 55 and serves to de-energize the auxiliary hold-up motors 48, 4? sequentially and also serves to decrease the separating force on the bridge in steps, the function being just the reverse of that occurring on the leading bridge and also occurring out of phase or time therewith. The phase relationship is determined by the angular spacing of the cylinder ports 27 for when one bridge has a cylinder port centered thereon the other bridge has a pair of cylinder ports 27 equally spaced from its center, and this phase relationship is illustrated by the position of the cylinder ports, FIG. 2, with respect to a diametrical line and by the results shown in the graph of FIG. 7.

It may be noted that if the cylinder unit is not rotating but is stopped in any position, that he proper balance of separating forces and hold-up forces is always maintained for the reason that the effective pressure field provided by the balance ports is matched with the area of the auxiliary hold-up motors for each bridge of the valve 28. It is necessary that the angular span between adjacent port extensions of valve ports 31, 32 :be slightly greater than the angular span of a cylinder port 27 so as not to be short circuited thereby when operating at slow speed as in the case of the machine being operated as a motor.

The function above described can be visually seen by superimposing a transparent copy of the cylinder wear plate of FIG. 2 coaxially on the flat valve of FIG. 3 and rotating to show different rotative positions between the two.

FIGS. 9 through 12 show another axially floating type of fiat valve 61 for a hydraulic machine operable as a pump which is driven in one direction as indicated by the arrow, FIG. 9, and at a constant and relatively high speed. The fiat valve 61 is stationary and is adapted for making fiuid sealing engagement with a rotatable cylinder barrel 14 or wear plate 26 therefore such as is shown in FIG. 2. The flat valve has relatively deep arcuate valve ports 63, 64 which have long and shallow port extensions 65, 66 extending in one direction, with respect to rotation of the cylinder barrel, and as shown extend midway of the bridges of the valve. The port extensions 65', 66 are formed by milled slots and serve as compression and decompression chambers in cooperation with cylinder ports crossing the bridges of the valve, and by reason thereof also modify the pressure field on the bridges of the valve. Since the machine will operate at relatively high speeds the cylinder port may overlap one port extension of one valve port and the other valve port to a slight extent.

The flat valve 61 is provided with flow through hold-up motors 36, 40 located under the valve ports 63, 64 and subject to the pressure of fluid in the valve ports for providing the main hold-up force for urging the fiat valve against the wear plate 26 in opposition to the separation forces there'between.

Three generally circumferentially spaced auxiliary hold-up motors 67, 68, 69 are positioned in the rear face of the valve in each radial section between the valve ports 63, 64. Hold-up motors 6'7, 69 are located substantially at the radial distance of the valve ports, and auxiliary hold-up motor 68 is intermediate the other two at a radial distance less than the radial distance of the valve ports in order to provide the necessary space therefore under the bridge of the valve. These auxiliary hold-up motors are preferably made of equal size and collectively provide an additional hold-up area to oppose the maximum increase in pressure field area on a bridge of the valve.

Three balance ports 71, 72, 73 are provided in the face of each bridge and are formed as by drilling or milling to effect balance areas which subdivide the field area of the bridge when successively communicating with a cylinder port crossing the bridge. Balance ports 71, 72, 73 are spaced circumferentially within the radius of the valve ports 63, 64 and radially inward of the port extensions 65, 66 which as shown lie on the radially outer edge of the valve ports. An additional balance area is provided in the face of each bridge by a balance area slot 74 milled in the face of the bridge on the radius of the port extensions radially adjacent to balance port 71. The balance slot 74 and the balance ports 71, 72, 73 are preferably milled to the same depth, which for the valve shown is on the order of of an inch. The intermediate balance port 72 is shown somewhat larger than each of the balance ports 71, 73 in order to provide the necessary balance of forces and moments.

Balance ports 71, 72, 73 in each bridge are connected respectively to the bridge cylinders 50 of auxiliary hold-up motors 67, 68, 69 by drilled holes 76, 77, 78, that are A; inch in diameter which is a relatively large diameter for such holes and permissible since they form part of the balance area of their respective balance ports.

The balance ports 71, 72, 73 are adapted to successively communicate with a cylinder port crossing a bridge so as to thereby extend the field of the cylinder port in steps as it crosses the bridge. A cylinder port registering with balance ports 72, 73 also registers with a port extension or 66, and a cylinder port registering with balance port 71 also registers with the additional balance area provided by balance slot 74. The balance ports 72, 73 taken with the adjacent port extension 65, 66, and the balance port 71 taken with balance slot 74 are thus constructed and arranged to predetermine stepped changes in the pressure field on the face of a bridge as a cylinder port crosses the bridge so that such stepped changes in the pressure field result in stepped changes in the separation forces between the fiat valve and cylinder wear plate 26 which are opposed by substantially equal and opposite additional hold-up forces provided by the corresponding auxiliary hold-up motors 67, 68, 69.

In operation, the flat valve which is non-rotatably supported, has cylinder ports moving clockwise on the face for the machine shown in FIG. 1, for the conventional direction of rotation of a pump is clockwise as viewed from the drive shaft 12 of the machine. With valve port 63 serving as the pressure port and valve port 64 as the return port, then a cylinder port 27 leaving valve port 63 is a pressure loaded cylinder port and moves on to the upper bridge of the flat valve, FIGS. 9 and 10, such a cylinder port 27 is shown superimposed on the flat valve, FIG. 10, as indicated by dashed lines thereon.

The pressure loaded cylinder port first communicates with balance port 71 and balance area slot 74 to provide a first step increase in the separation forces on the face of the upper bridge of the fiat valve. Then the cylinder port in moving further communicates with balance port 72 to provide a second step increase in the separation force on the face of the upper bridge. A third successive positioning of the cylinder port brings it into communication with balance port 73 and port extension 66 of the return port, at which position the cylinder port no longer communicates with the pressure valve port 63. In initiating this third position, the cylinder port which has been pressure loaded, pressurizes the balance port 73 and its associated bridge cylinder 50 of auxiliary hold-up motor 69 at a pressure reduced from normal value because of leakage flow into port extension 66 which has begun to decompress the cylinder port. Nevertheless, in the third position, the cylinder port provides a step change in the separation force that is balanced by its auxiliary hold-up motor 69.

Similarly, a cylinder port whose working piston nears the end of its suction stroke is leaving suction valve port 64 and beginning to cross the lower bridge of the flat valve. This cylinder port first engages balance port 71' and balance area slot 74' and next communicates with balance port 72' while also still communicating with balance port 71, balance area slot 74' and suction valve port 64. Continued further movement of the cylinder port brings it into communication with balance port 73' and out of communication with suction valve port 64 and in communication with pressure port extension 65. The latter port extension 65 serves to gradually raise the pressure in the cylinder port as the cylinder port moves there-across toward the pressure port.

Cylinder ports crossing the bridges of the valve sequentially communicate with the balance areas on the face of the bridges of the fiat valve provided by the balance ports 71, 72, 73 and balance area slot 74 on the upper bridge and provided by the balance ports 71, 72', 73' and balance area slot 74' on the lower bridge to provide stepped changes in the separation forces that are substantially equal and opposite to the changes in the hold-up forces provided by the corresponding auxiliary hold-up motors. While the changes that take place on one bridge are out of phase with those on the opposite bridge, the arrangement is such as to make the characteristics of the separation forces closely follow the characteristics of the hold-up forces so that a very small net positive hold-up force is maintained on the fiat valve which may be on the order of a few pounds instead of hundreds of pounds.

While one flat valve is-shown having two balance ports in each bridge and for operation of the hydraulic machine in either direction of rotation at variable speeds, as a motor; and another fiat valve is shown having three balance ports in each bridge and for operation of the hydraulic machine at a constant relatively high speed for one direction of rotation, as a pump, various changes may be made therein which will be within the spirit of the invention and the scope of the claims.

We claim:

1. A hydraulic machine comprising a rotatable cylinder unit having coaxial valve seat with circumferentially spaced cylinder ports, a fiat valve arranged with a face in sealing engagement with the valve seat and having diametrically opposite arcuate high and low pressure ports and subject to changing hydraulic forces and moments tending to separate the valve from the valve seat due to changes in the area of the pressure field therebetween for different angular positions of the cylinder unit, hold-up motors under the ports of the valve and subject to the pressure in their associated ports to provide a main holdup force substantially equal and opposite to a minimum separation force that occurs between the valve and valve seat, the intermediate circumferential portions of the valve between the high and low pressure ports being the bridges of the valve, auxiliary hold-up motors under the bridges adapted to be energized to provide auxiliary hold-up forces which with the main hold-up force are substantially equal and opposite to the maximum separating forces, characterized in that each bridge has a plurality of separate said auxiliary hold-up motors generally circumferentially spaced and adapted to sequentially communicate with a cylinder port crossing the bridge to provide stepped changes in the auxiliary hold-up forces,

separate balance ports in the face of each bridge and generally circumferentially spaced and separately connected to corresponding said auxiliary hold-up motors and adapted to register with a cylinder port crossing the associated said bridge,

said balance ports defining predetermined areas effective upon registering with a cylinder port to establish stepped changes in the separating forces corresponding to the stepped changes in the auxiliary hold-up forces, whereby the centroids of opposing forces very closely follow one another.

2. A hydraulic machine according to claim 1 in which the balance ports in each bridge effectively divide the bridge into two field areas corresponding to the hold-up areas of their associated auxiliary hold-up motors so that upon communication of a cylinder port with a balance port the resulting changes in the separation forces are maintained substantially equal and opposite to the changes in the hold-up forces provided by the auxiliary hold-up motors which communicate with the cylinder port crossing the bridge.

3. A hydraulic machine as defined in claim 1 in which there are two said auxiliary hold-up motors under each bridge so as to change the auxiliary hold-up forces in two steps as a cylinder port crosses the associated bridge and there are two said balance ports in the face of the bridge to establish a two step change in the separation forces that correspond to and are balanced by the changes in 10 the auxiliary hold-up forces; whereby the valve remains substantially balanced with a minimum of difference between the separation and hold-up forces for any angular position of the cylinder unit.

4. A hydraulic machine as defined in claim 1 in which the auxiliary hold-up motors circumferentially spaced under each bridge effect a three stepped increase in the auxiliary hold-up forces under a leading one of the bridges upon which a cylinder port moves from the high pressure valve port, and the corresponding balance ports on the leading bridge are arranged to cooperate with the maximum increase in the pressure field on the leading bridge in three steps to establish a corresponding three stepped increase in the separation forces substantially equal and opposite to the stepped increases in the auxiliary hold-up forces for the leading bridge.

5. A hydraulic machine comprising a rotatable cylinder unit having coaxial valve seat with circumferentially spaced cylinder ports, a flat valve arranged with a face in sealing engagement with the valve seat and having diametrically opposite arcuate high and low pressure ports and subject to changing hydraulic forces and moments tending to separate the valve from the valve seat due to changes in the area of pressure field therebetween for different angular positions of the cylinder unit, hold-up motors under the ports of the valve and subject to the pressure in their associated ports to provide a main holdup force substantially equal and opposite to a minimum separation force that occurs between the valve and valve seat, bridges of the valve being the face thereof between the valve ports and bridge sections of the valve being radial sections including the bridges thereof, auxiliary hold-up motors under each bridge section adapted when energized to provide additional hold-up force urging the valve toward the valve seat, said valve characterized in that the valve ports each have a long leading slot serving as a port extension extending in one direction substantially midway of the bridges for leading communication of each valve port with cylinder ports crossing the bridges and adapted for a cylinder unit having one direction of rotation, three generally circumferentially spaced said auxiliary hold-up motors in each bridge section, three similarly constructed large balance area recesses circumferentially spaced in each bridge and individually connected to corresponding said auxiliary hold-up motors and adapted to sequentially register with cylinder ports crossing the bridge, an additional balance area formed by a balance slot in the line of the port extension in the face of each bridge and radially adjacent that one of the balance area recesses remote from the port extension, whereby the port extension, the balance area recesses and the additional balance slot cooperate with cylinder ports crossing the bridge to cause the hydraulic separation forces to vary in three steps corresponding to the three step change in the additional hold-up forces provided by the auxiliary hold-up motors so that the separation forces and their moments are always balanced by the hold-up forces and their moments.

6. A hydraulic machine comprising a rotatable cylinder unit having a coaxial valve seat with circumferentially spaced cylinder ports therein, an axially floating fiat valve having diametrically opposite arcuate high and low pressure valve ports with which the cylinder ports alternately register upon rotation of the cylinder unit, the valve ports defining therebetween the bridges of the valve, means hydraulically balancing the flat valve on the valve seat when the hydraulic forces therebetween are a minimum, a plurality of bridge motors under each bridge of the valve aiding in hydraulically balancing the valve on the seat when the hydraulic forces therebetween are a maximum,

said flat valve characterized in that there are not more than three said bridge motors under each bridge which are circumferentially spaced from each other, balance area recesses circumferentially spaced from 11 12 each other in the face of each bridge and individually thereto; whereby the centroids of opposing forces connected to correspondingly spaced said bridge movery closely follow each other. tors, respectively, said balance area recesses constructed and arranged References filed y the EXamillel' witl'tl respectftol said bridge nrotorsflsloflthabt cylinder 5 UNITED STATES PATENTS por sequen 1a y commumca es W1 e a ance area recesses and bridge motors in one bridge while a geng et a1 1O3 161 erally opposite cylinder port, in accordance with the 4 41 8/1958 ggg 103-162 angular phase relationshlp therebetween, sequentral- 3,037,489 6/1962 Douglas 103 162 X ly communicates with the balance area recesses and 10 bridge motors in the other bridge, so that each of said balance area recesses upon communication with SAMUEL LEVINE Prmmry Exa'mner' a cylinder port provides a step-change in the pres- LAURENCE E minersure field opposing a step-change in the hold-up area C. MUNRO Assistant Examiner provided by the individual bridge motor connected 15 

1. A HYDRAULIC MACHINE COMPRISING A ROTATABLE CYLINDER UNIT HAVING COAXIAL VALVE SEAT WITH CIRCUMFERENTIALLY SPACED CYLINDER PORTS, A FLAT VALVE ARRANGED WITH A FACE IN SEALING ENGAGEMENT WITH THE VALVE SEAT AND HAVING DIAMETRICALLY OPPOSITE ARCUATE HIGH AND LOW PRESSURE PORTS AND SUBJECT TO CHANGING HYDRAULIC FORCES AND MOMENTS TENDING TO SEPARATE THE VALVE FROM THE VALVE SEAT DUE TO CHANGES IN THE AREA OF THE PRESSURE FIELD THEREBETWEEN FOR DIFFERENT ANGULAR POSITIONS OF THE CYLINDER UNIT, HOLD-UP MOTORS UNDER THE PORTS OF THE VALVE AND SUBJECT TO THE PRESSURE IN THEIR ASSOCIATED PORTS TO PROVIDE A MAIN HOLDUP FORCE SUBSTANTIALLY EQUAL AND OPPOSITE TO A MINIMUM SEPARATION FORCE THAT OCCURS BETWEEN THE VALVE AND VALVE SEAT, THE INTERMEDIATE CIRCUMFERENTIAL PORTIONS OF THE VALVE BETWEEN THE HIGH AND LOW PRESSURE PORTS BEING THE BRIDGES OF THE VALVE, AUXILIARY HOLD-UP MOTORS UNDER THE BRIDGES ADAPTED TO BE ENERGIZED TO PROVIDE AUXILIARY HOLD-UP FORCES WHICH THE MAIN HOLD-UP FORCE ARE SUBSTANTIALLY EQUAL AND OPPOSITE TO THE MAXIMUM SEPARATING FORCES, CHARACTERIZED IN THAT EACH BRIDGE HAS A PLURALITY OF SEPARATE SAID AUXILIARY HOLD-UP MOTORS GENERALLY CIRCUMFERENTIALLY SPACED AND ADAPTED TO SEQUENTIALLY COMMUNICATE WITH A CYLINDER PORT CROSSING THE BRIDGE TO PROVIDE STEPPED CHANGES IN THE AUXILIARY HOLD-UP FORCES, SEPARATE BALANCE PORTS IN THE FACE OF EACH BRIDGE AND GENERALLY CIRCUMFERENTIALLY SPACED AND SEPARATELY CONNECTED TO CORRESPONDING SAID AUXILIARY HOLD-UP MOTORS AND ADAPTED TO REGISTER WITH A CYLINDER PORT CROSSING THE ASSOCIATED SAID BRIDGE, SAID BALANCE PORTS DEFINING PREDETERMINED AREAS EFFECTIVE UPON REGISTERING WITH A CYLINDER PORT TO ESTABLISH STEPPED CHANGES IN THE SEPARATING FORCES CORRESPONDING TO THE STEPPED CHANGES IN THE AUXILIARY HOLD-UP FORCES, WHEREBY THE CENTROIDS OF OPPOSING FORCES VERY CLOSELY FOLLOW ONE ANOTHER. 